Radio Frequency (RF) transmitters are used to transmit RF signals. The RF signals can convey many types of information, such as digital and analog communications and radio direction and ranging (RADAR) information. Many examples of uses for RF transmitters are found in aircraft. One such example of an RF transmitter is that of an Aviation Collision Avoidance System.
The RF transmitter used in the Aviation Collision Avoidance System typically includes a transmitter circuit and a modulator circuit. The transmitter circuit and the modulator circuit are each typically developed on individual printed circuit boards (PCB). The printed circuit board used by the modulator circuit, or modulator circuit board, may have a ground plane attached to a surface of the printed circuit board for providing a ground reference potential to certain components of the modulator circuit. The printed circuit board used by the transmitter circuit, or transmitter circuit board, is connected to a metal chassis that encases the transmitter. The metal chassis provides a ground reference potential to certain components of the transmitter circuit. The transmitter circuit includes a power transistor that supplies power to certain components of the transistor circuit. A base of the power transistor is electrically connected to the chassis. The power transistor is either laminated or xe2x80x9cvapor-phasedxe2x80x9d with a corrosion inhibitor. The laminate isolates the ground reference potential from certain components of the transmitter circuit board. Ground isolation prevents xe2x80x9ccross-talkxe2x80x9d between components of the transmitter and the power transistor. The laminate also provides corrosion protection to the transmitter circuit board.
Separating a modulator circuit board from a transmitter circuit board increases design complexity. However, the ground reference potential supplied by the metal chassis is necessary to improve output power of the power transistor and prevent xe2x80x9cfrequency-pullingxe2x80x9d of the transmitted signal. xe2x80x9cFrequency-pullingxe2x80x9d is an unintentional alteration of a transmitted signal at the transmitter end of a communication link. The unintentional alteration of the transmitted signal degrades reception capabilities at a receiver end of the communication link. Present grounding techniques cannot offer a combined transmitter-modulator circuit board that supplies a ground reference potential for preventing xe2x80x9cfrequency-pullingxe2x80x9d of the transmitted signal. Moreover, the present grounding techniques of the combined transmitter modulator circuit board degrade output power for the transmitter circuit, thereby decreasing strength and, thus, reception capabilities of the transmitted signal.
Transmitters are often essential to safety, particularly when used in aviation systems. Transmitters used in the Aviation Collision Avoidance Systems ensure that aircraft do not collide with one another by transmitting proximity information to the aircraft. The proximity information includes details about aircraft in an area, such as location, altitude, and speed of nearby aircraft. Proper transmission of the proximity information assists in reception of the proximity information. Poor or missed receptions of the proximity information can result in catastrophic events.
The invention provides certain features to advance the state of the art by providing, among other features, a circuit for transmitting RF signals that supplies a ground reference potential to a transmitter component and a modulator component. Other features will be apparent in the description that follows.
In one aspect, the invention provides a circuit on a printed circuit board for transmitting radio frequency (RF) signals. A modulator operatively coupled to the printed circuit board modulates a signal to be transmitted by modulating an information signal onto a carrier signal. A ground plane attaches to edges and to first and second surfaces of the printed circuit board. The ground plane electrically connects to components of the modulator. A power transistor physically attaches to the printed circuit board and electrically connects to the ground plane through a slot in the printed circuit board. The ground plane provides a suitable ground reference potential for both the modulator and the power transistor without individually constructed circuit boards for each. A ground isolation barrier formed with the ground plane may prevent xe2x80x9ccross talkxe2x80x9d between the modulator and the power transistor. The ground isolation barrier may prevent unintentional connection to the ground plane by other components that may be attached to the printed circuit board.
In another aspect, the modulator electrically connects to the ground plane through vias of the printed circuit board. A metal connector may physically connect the power transistor to the printed circuit board through the slot in the printed circuit board. The metal connector may contact the ground plane to electrically connect the power transistor to the ground plane such that the power transistor receives the ground reference potential. A grounding strap may attach to the metal connector and electrically connect to the ground plane. A heat sink may attach to the ground plane with the metal connector to dissipate heat from the circuit.
The circuit provides an improved ground reference potential to the power transistor, which can improve the gain of a transmitted signal. The circuit also increases frequency stability of the transmitted signal by decreasing external inductance to the power transistor.